Axial flow pump with multi-grooved rotor

ABSTRACT

An axial-flow blood pump for pumping blood includes a substantially cylindrical outer enclosure. A tubular housing concentric with and located within the outer enclosure has at one end an inlet and at an opposite end an outlet. A motor stator is concentric with and located between the outer enclosure and the tubular housing. An impeller is concentric with and located within the tubular housing. The impeller is suspended in operation by a combination of passive magnetic forces between magnets within the impeller or magnetized regions of the impeller and the motor stator and hydrodynamic thrust forces generated as blood flows between the tubular housing and a plurality of hydrodynamic thrust bearing surfaces located on the impeller. A volute may be in fluid-tight connection with the outlet of the tubular housing for receiving blood in the axial direction and directing blood in a direction normal to the axial direction. The volute has a flow-improving member extending axially from the volute and into and coaxially with the tubular housing.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of: U.S. applicationSer. No. 11/003,810, filed Dec. 3, 2004; PCT International ApplicationNo. PCT/US2005/042495, filed Nov. 22, 2005; U.S. Application Serial No.11/118,551 filed Apr. 29, 2005; PCT International Application No.PCT/US2005/035964, filed Oct. 6, 2005; and U.S. application Ser. No.11/243,722, filed Oct. 5, 2005. The contents of each of the foregoingapplications is hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present disclosure relates to rotary pumps and, in particular, toaxial flow blood pumps having a generally cylindrical rotor suspendedwithin a corresponding cylindrical housing having a blood inlet at oneend and blood outlet at another end, and motor components to providerotational energy to spin the rotor and pump blood fluid longitudinallythrough the housing from the housing inlet to the housing outlet.

BACKGROUND OF THE INVENTION

The known axial flow pumps for blood have the advantage of narrow radialwidth, when compared with centrifugal flow pumps. They may therefore beused for intra-vascular or intra-heart blood pumping assistance. Axialflow pumps typically have a cylindrical housing with an inlet at oneend, an outlet at the opposite end, and a rotor within the housing whichhas thin impeller blades or vanes attached to and protruding radiallyoutwardly from the rotor. Thus, as the rotor rotates, the blades addwork to the fluid, propelling the fluid through the housing from thehousing inlet to the housing outlet.

A suspension system is provided to maintain the rotor in a desiredposition within the housing, and an electromagnetic motor is provided tospin the rotor. The rotor may be mechanically, magnetically orhydrodynamically suspended within the blood flow passage. A combinationof such suspension techniques may be utilized.

Typically in the prior art, the rotor is suspended by mechanicalbearings or bushings, some with a rotor shaft protruding through thepump housing to a motor drive mechanism. Magnetic suspension is alsoknown, as in U.S. Pat. Nos. 6,368,083 and 5,840,070. The blooddischarged from the pump, flows parallel to the axis of rotation of therotor.

Axial blood flow pumps have heretofore used a thin blade design, withthe motor magnets being placed either in the rotor shaft, relatively faraway from the surrounding stator, as in pumps by Jarvik and Incor, orthey use small magnets placed within the thin blades, as in a pump madeby MicroMed. Both of these approaches tend to reduce the motor torquecapacity and efficiency, and they require mechanical rotor supportinvolving abutting surfaces that move and wear against each other inrotation.

It is desirable for blood pumps, whether internally or externallylocated, to be more tolerant of flow variations than the previous thinblade designs and to exhibit low hemolysis, good resistance tothrombosis, adequate system efficiency, and very high reliability forthe expected duration of use for the device. Internally located bloodpumps are also subject to anatomical compatibility design constraintsand the need for elimination of mechanical wear and associated failuremodes in order to provide successful, long-term, implantable devices.

While the pump of this invention is described in terms of a blood pump,it is also contemplated that the pump might be used for pumpingchemically difficult fluids or non-magnetic fluids, where a seallessdesign is highly desirable, and the fluid must be gently handled forvarious reasons, for example because it is unstable to mechanicalstress, causing decomposition and even explosiveness, or because it isanother complex, biological fluid besides blood, having criticalstability parameters.

SUMMARY OF THE INVENTION

In accordance with the present invention an axial flow sealless andwearless blood pump is provided which comprises a tubular pump housinghaving a blood inlet at one open end and a blood outlet at the otheropen end opposite the inlet. A cylindrical rotor is suspended within thehousing tube. The rotor comprises a plurality of peripheral and radialsurfaces to engage and create pressure to assist in movement of theblood through the housing from the inlet end to the outlet end. A motoris provided to cause the rotor to spin within the housing. In oneembodiment, the motor stator includes electrically conductive coilslocated external to or within the housing tube. A plurality of magneticmotor drive poles is provided on the rotor, spaced about its peripheralsurfaces. The stator coil provides magnetic flux to cause the rotor tospin.

The rotor comprises a cylindrical body having a leading edge portion forengaging blood entering the housing at the inlet and a trailing edgeportion for enhancing the discharge of the blood at the outlet of thehousing. The rotor comprises one or more grooves each extending from anentry channel at the leading edge portion of the rotor to an exitchannel at the trailing edge portion so as to define a plurality ofarcuate peripheral land areas therebetween on the surface of the rotor.The sidewall surfaces defining each groove extend radially to the rotorsurface but are not necessarily parallel to each other. In someembodiments each groove has a central portion defining a flow channelcurved at least partially around the rotational axis of the rotor and influid flow communication with a substantially axially directed channelat the trailing edge portion of the rotor. The sidewalls of the groovesadd axial thrust to the blood when the rotor is spinning and impart arotational momentum to the flow of blood downstream of the rotor. Insome embodiments, the central portion of each groove defines a narrowerflow channel than is provided at its entry and exit channels. In someembodiments each groove is wider at its exit channel than at its entrychannel to enhance the exit flow characteristics of the blood. In oneembodiment, the combined total width of the central portions of thegroove flow channels is substantially equal to or less than thecollective, total arcuate widths of the peripheral land areas formedbetween the groove flow channels. The flow channels along the rotor maybe helical along some portions of the rotor and generally axial directedalong other portions of the rotor.

A plurality of hydrodynamic thrust bearing surfaces is provided on eachof the peripheral surfaces of the land areas of the rotor. The bearingsurfaces create fluid pressure at the periphery of the rotor therebyimparting radially symmetrical forces to the rotor, which maintain theradial position of the rotor within the housing when the rotor isspinning, and to provide good washing near the surrounding housing forincreased resistance to thrombosis.

The land surface areas of the rotor between the flow channels of thegrooves are each wider and longer at their peripheries than the thinblades of prior art axial flow blood pumps. This permits the emplacementor formation of relatively large motor drive magnets at or near theperiphery of the rotor. Large drive magnets in the rotor increasemagnetic force, and their placement at the rotor periphery reduces thegap between the magnetic poles of the rotor and magnetic flux generatingcoils of a motor stator. This arrangement improves motor torque capacityand electromagnetic efficiency of the pump. Axial magnetic stiffnessprovided by a motor of radial flux gap design may be used to assist inholding the rotor in its axial position within the housing.

A magnetic bearing system may be provided, as well as hydrodynamicthrust bearings, to help maintain the position of the rotor radially oraxially within the tubular housing. Magnetic poles to assist insuspension of the rotor within the housing may be placed within theperipheral land surfaces between the grooves of the rotor to beattracted to or repelled by corresponding magnetic poles within oradjacent the surrounding pump housing.

In one embodiment, magnetic bearings may be used instead of hydrodynamicthrust bearings, to provide an all magnetic suspension system. Suchmagnetic bearings could be positioned or formed in the peripheral landareas of the rotor either forward or aft of the location of the motordrive magnets. Accordingly, a rotor in accordance with this inventiondoes not require mechanical supporting structures upstream or downstreamthereof. Hydrodynamic thrust bearings, with or without magneticbearings, or exclusive magnetic bearings, will be sufficient to maintainthe rotor in desired position during operation.

In some embodiments, the configuration of the tubular pump housing mayinclude an annular sloped interior surface near the rotor's leading ortrailing edge portions to provide a mechanical stop for axial movementof the rotor. Such a configuration provides additional axial support forthe rotor, as may become necessary in the event of shock loading toensure that the rotor remains in proper position within the housing.

Alternately, a split housing configuration might be provided, withannular sloped surfaces at both the rotor leading and trailing edgeportions, to provide radial support and axial support in both axialdirections. The blood pump may also utilize one or more upstream anddownstream flow straighteners or diffusers to enhance flowcharacteristics of blood as it enters or exits the pump.

A controller is provided to run the motor at a set rotational speed,which may be set, for example by the attending physician. Alternatively,the motor may be run at a rotational speed which varies in response to aphysiological control algorithm.

Unlike axial flow pump designs heretofore using radial thin bladeimpellers, upstream and downstream struts or stator elements which mayserve as flow straighteners or diffusers may be useful but are notrequired. The absence of these upstream and downstream flowstraighteners permits a simpler mechanical design, with fewer axialtolerance concerns associated with their placement. Moreover, theabsence of upstream flow straighteners or diffusers permits a pre-swirlto the upstream blood flow pattern that may serve to improve resistanceto thrombosis.

In some embodiments, a volute may be used at the output end of thehousing to improve the output flow characteristics of the blood. Forexample, a volute may be used to redirect the blood flow in a directionnormal to the rotational axis of the pump. A volute may improve theoutput blood flow characteristics of an axial flow pump by convertingrotational kinetic energy in the output flow from the axial flow pump toa slower output velocity having sufficient pressure for discharge intothe vascular system.

The blood pump of this invention might be implanted within the vascularsystem or located within the chest cavity of a patient, such as thepericardial space, abdomen, or subcutaneously near the skin, in a mannersimilar to pacemaker implantation. Likewise, the pump may be keptexternal to the body for shorter term vascular circulatory support. Alsomulti-rotor or ganged rotor pumps having a plurality of axially alignedaxial flow pumps of the type described herein could be used to providesingle or bi-ventricular support, or even total circulation for thepatient in the manner of a full, artificial heart. Moreover, suchmulti-stage pumps can be constructed with smaller diameter tubularhousing for intra-vascular implantation.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and many of theattendant advantages thereof will be better understood by reference tothe following detailed description when considered in connection withthe accompanying drawings, wherein:

FIG. 1 is a longitudinal sectional view of an implantable, sealless,axial rotary blood pump in accordance with this invention.

FIG. 2 is an elevational side view of a rotor of the rotary pump of FIG.1.

FIGS. 3 and 4 are elevational views of two different sides of the rotorof FIG. 2.

FIG. 5 is a sectional view taken along line 5-5 of FIG. 2, with internalparts omitted.

FIG. 6 is a perspective view of an alternative embodiment of a rotorusable in the pump of this invention.

FIG. 7 is a rear perspective view of a rotor of the embodiment of FIG.1.

FIG. 8 is a top perspective view of the rotor of FIG. 7.

FIG. 8A is an enlarged, fragmentary, perspective view of a portion ofthe rotor of FIG. 7.

FIG. 8B is an exploded view of an embodiment of the rotor of FIG. 7.

FIG. 9 is a longitudinal sectional view of an alternate embodiment ofthe pump of FIG. 1.

FIG. 10 is a plan view, taken partially in longitudinal section, showinga multiple-rotor blood pump of the present invention.

FIG. 10A is a plan view of another embodiment of the blood pump of FIG.10.

FIG. 11 is an exploded view of an alternate embodiment of the axial flowblood pump of the present invention.

FIG. 11A is a perspective view of a motor stator of the embodiment ofFIG. 11.

FIG. 12 is a schematic sectional view of a blood pump with a voluteaccording to an embodiment of the present invention.

FIG. 13 is a perspective view of the blood pump with a volute shown inFIG. 12.

FIG. 14 is an exploded view of the blood pump with a volute shown inFIG. 12.

FIG. 15 is a perspective view of the interior of a volute according toone embodiment of the present invention.

FIG. 16 is a top plan view of the interior of the volute shown in FIG.15.

FIG. 17 is a perspective view of the interior of a volute according toanother embodiment of the present invention.

FIG. 18 is a perspective view of the interior of a volute according to afurther embodiment of the present invention,

FIG. 19 is a perspective view of the interior of a volute according toyet another embodiment of the present invention.

FIG. 20 is a perspective view of a downstream flow straighteneraccording to still another embodiment of the present invention.

FIG. 20A is bottom elevation view of the flow straightener shown in FIG.20.

FIG. 21 is a perspective view of a downstream flow straighteneraccording to a still further embodiment of the present invention.

FIG. 22 is a perspective view of a downstream flow straighteneraccording to a yet further embodiment of the present invention.

FIG. 22A is a bottom elevational view of the flow straightener shown inFIG. 22.

FIG. 22B is side elevation view of the flow straightener shown in FIG.22.

FIG. 23 is a perspective view of a downstream flow straighteneraccording to yet another embodiment of the present invention.

FIG. 23A is a bottom plan view of the flow straightener shown in FIG.21A.

FIG. 24 is a perspective view of an artificial heart utilizing axialflow rotary pumps of the type shown and described herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In describing the preferred embodiments of the present disclosureillustrated in the drawings, specific terminology is employed for sakeof clarity. However, the present disclosure is not intended to belimited to the specific terminology so selected, and it is to beunderstood that each specific element includes all technical equivalentswhich operate in a similar manner.

Referring now to the drawings and in particular o FIGS. 1-5, anembodiment of a blood pump 10 adapted to assist in pumping blood througha patient's vascular system is disclosed, comprising a hollow generallytubular pump housing 12. The pump housing 12 is non-magnetic and is madeof a suitable biocompatible material such as titanium or a suitableceramic material which is non-thrombogenic, rigid and exhibits minimumeddy current lossess. The housing 12 defines a blood inlet end II and ablood outlet end 11A so that blood flows through the housing in thedirection shown by the arrow 18. In one embodiment the housing 12 has aconstant exterior diameter while the inlet portion of its interiordiameter first converges as indicated at 13 and thereafter diverges asat 13A to define an annular hump or ring, indicated in FIG. 1 byreference numeral 52.

A substantially cylindrical rotor 14 is positioned within the lumen ofthe pump housing 12, and acts as an impeller for pumping fluid withinthe housing. In one embodiment, the rotor 14 is provided with a taperedleading edge 14A which is contoured to follow the diverging portion 13Aof the interior diameter of the housing. The converging and divergingdiameter portions 13 and 13A may act as a mechanical stop to maintainthe rotor 14 in proper axial position within the tubular housing if, forexample, an external shock would tend to jolt the rotor out of itsworking axial position. In some embodiments the tapered leading edge 14Aof the rotor may be provided with a hydrodynamic thrust bearing surfaceof the type described below to cooperate with the surface of thediverging diameter portion 13A of the housing 12 for additionalprotection against axial shock loading. The alignment between thehousing diverging diameter portion 13A and the tapered leading edge 14Aof the rotor could also be utilized to provide a magnetic axial preloadat the rotor's leading edge, similar to that described below withrespect to its trailing edge, to assist the rotor in maintaining itssuspended and wearless position within the housing.

Rotor 14 comprises one or more grooves 22 each of which extends from anentry section or inlet channel 22A at the leading edge 14A to an exitsection or outlet channel 22B at the trailing edge 14B of the rotor. Thegrooves 22 define fluid flow channels across the rotor. In someembodiments a plurality of grooves 22 formed in the rotor 14 are spacedapart and define plurality of peripheral land areas 35 therebetween.Each groove is defined by a pair of side walls 16 extendingsubstantially radially to the rotational axis of the rotor, but notnecessarily parallel to each other.

As shown in FIGS. 1-4 and 6, each of the grooves 22 has a central flowchannel 30 that curves at least partially around the rotational axis ofthe rotor and opens into a substantially axially extending outletchannel 22B. The curved central portion 30 is narrower than the inletchannel 22A or outlet channel 22B. The relatively wide outlet channeland its axial orientation enhances the discharge flow characteristics ofthe blood being pumped by more easily allowing for the release of bloodfrom the rotor. The grooves 22 and their side walls 16 tend to driveblood in the axial direction, shown by the arrow 18, as the rotor 14 isrotated (clockwise in the embodiment of FIG. 1).

In one embodiment, the number of grooves 22 may be in the range of from2 to 8, with four being typical. irrespective of the number of grooves,their collective widths at the outer periphery 23 of the rotor 14 (FIG.5) is equal to or substantially less than the collective, totalcircumferential width at the same outer periphery 23 of all of the landareas 35 defined between the grooves. By way of example, as shown in theembodiment of FIG. 5, the peripheral width of a groove 22 at the crosssection of the rotor taken along the line 5-5 of FIG. 2 is shown by thearrow 26. The arrow 26 is shorter than the width of an adjacent landsection 35 as measured by the length of the arc 28. Collectively, at thecentral portions along the grooves 22, the total width of the grooves 22is less than or equal to the collective, total width of the respectiveland areas 35.

In this embodiment, the depth of each of the grooves 22 is greater thanthe radial extent of the blades in comparable and conventional thinblade axial pump designs. For example, for heart pump uses, the averagedepth of the grooves 22 from their outer perimeters may fall within therange of from 1 mm to 5 mm. In some embodiments the average depth of thegrooves is approximately ⅓ the diameter of the rotor, but is less thanthe radius of the rotor. In other embodiments the grooves may be deeperat the entry channel 22A at the leading edge of the rotor and shallowerat the exit channel 22B at the trailing edge of the rotor.

With reference to FIG. 2, the blood pump 10 further comprises a rotor,which includes a plurality of relatively large permanent drive magnets34 (shown in dotted lines) formed within each of the wide land areas 35of the rotor 14. According to one embodiment of the present invention,the permanent drive magnets 34 in the rotor may be produced bymagnetizing selected portions of the peripheries of the land areas 35.This may be accomplished, for example, by constructing the rotor from amagnetic alloy, which may be isotropic, and magnetizing desiredperipheral sections to form a plurality of magnetic poles with variousgeometric orientations. It is preferable to use a magnetic alloy that isbiocompatible so that no additional coating is required. Such a rotormay be easier and less expensive to manufacture than impellers formedfrom multiple parts.

With reference to FIG. 1, the motor also comprises a motor stator 36having electrically conductive coils 38. The coils are placed within anenclosure 40 which surrounds the tubular housing 12 and the rotor 14.The motor stator 36 serves to rotate rotor 14 by the conventionalapplication of electric power to the coils 38 to create magnetic flux.The permanent drive magnets incorporated into the wide land areas 35 ofthe rotor are selected for magnetic properties, length, andcross-sectional area in order to provide good electromagnetic couplingwith the magnetic flux created by the motor stator. Because of therelatively large surface area of the land areas, the nature andplacement of the rotor magnets becomes relatively easy to effect. Thisarrangement provides strong electromagnetic coupling and the necessarymagnetic axial stiffness to maintain the rotor in position. In oneembodiment, the magnetic coupling between the stator flux and the drivemagnets in the rotor creates torque, causing the rotor 14 to rotateclockwise. It will be understood by those skilled in the art that therotor could be caused to rotate in a counterclockwise direction withoutdeparting from the scope of the invention.

The motor may be a three phase, brushless DC motor. In one embodimentthe motor could be a toroidal, three phase and wye connected design. Thestator may have a back iron design which is consistent with a typicalradial flux gap motor. If desired, the motor stator can comprise aseparate, hermetically sealed enclosure 40 that slides over the tubularhousing 12 into position. A braised weld ring to the enclosure 40 outersurface may be used to secure the motor stator housing in position.Laser welding is one possibility for securing the motor stator enclosure40 to the housing and obtaining a hermetic seal. The specific technologyfor accomplishing this known in the prior art.

Referring to FIG. 6, another embodiment of a rotor 14 b for the bloodpump of this invention is disclosed. Rotor 14 b is shown to have sixperipheral land sections 35 b between the flow channels 22 havingcentral portions 30. Otherwise, the nature and configuration of therotor 14 b is similar to the rotor of the other embodiments disclosedherein.

Referring to FIGS. 7, 8, and 8A, there is depicted a rotor 14 which issimilar to the rotor shown in the embodiment of FIGS. 1-5. Theperipheral land areas 35 of the rotor 14 are each provided with one ormore hydrodynamic thrust bearing surfaces 44 and 46. Each of the thrustbearing surfaces 44, 46 is disposed along the surface of the associatedland area having a prescribed peripheral radius. The leading edge 47 ofeach of the bearing surfaces from the viewpoint of the (clockwise) spinof the rotor 14, is recessed by a predetermined amount below the surfaceof the associated land section, as depicted in FIGS. 8 and 8A byreference numeral 45. The recessed surface then tapers in a gradual,curved manner across the land area along an arc, the axis of curvatureof which is not necessarily co-axial with the rotational axis of therotor. The tapered bearing surface terminates at a rear end 48, at whichpoint each bearing surface 44, 46 is feathered into the periphery of theland area with a smooth transition and is no longer recessed withrespect to the continuing downstream surface of the land area.

As the rotor rotates, the respective thrust bearings, 44, 46 on eachland area 35 scoop blood onto the bearing surfaces whereby it flowsbetween the bearing surfaces and the inner wall of the tubular pumphousing. The effect of the tapered configuration of the thrust bearingsurfaces is to force blood to flow through a decreasing or constrictingarea created between the bearing surfaces and the inner wall of thetubular pump housing.

This results in increasing fluid pressure upstream within theconstriction, which pressure acts against the bearing surface areas andproduces a net symmetrical force for radial support of the spinningrotor. That hydrodynamic thrust bearings act in this way to cause radialpressure on a rotor is well known to the art generally, as in U.S. Pat.No. 5,840,070. The hydrodynamic force that is thus created on thesurfaces of the rotor land areas tends to hold the rotor suspended andcentered within the lumen of the tubular housing 12 in a manner shown inFIG. 1, and resists dynamic, radial shock loading forces without theneed for physically contacting bearing surfaces. The thrust bearingsurfaces 44 and 46 may be formed directly into the peripheral surfacesof the land areas 35 or may be placed within suitable cavities formed inthe outer peripheral surfaces of the land areas and held in place by asuitable cover.

In some embodiments, hydrodynamic thrust bearing surfaces are created onthe leading or trailing edge portions of the rotor. For example, withreference to FIGS. 1-3, the surface area 20 at the leading edge 14A ofthe rotor is tapered into a suitable thrust bearing configuration tocooperate with the diverging interior surface 13A of the tubular pumphousing. Such a thrust bearing would resist longitudinal movement of therotor to the left, as shown in FIG. 1. Alternatively, the divergingportions 13A partially defining the annular ring 52 may, if desired,comprise hydrodynamic thrust bearings cooperating with the adjacentrotor surface to prevent contact between the rotor 14 and the ring 52 asthe rotor operates in a clockwise rotation.

Hydrodynamic thrust bearing surfaces may also be located on the rotornear its trailing edge 14B, in which event the inner diameter of thetubular pump housing near its outlet end 11A would be constricted asshown in dotted lines in FIG. 1 to define an annular ring 53 similar tothe ring 52 near the inlet end 11. Such thrust bearings on the rotor orformed on a side of the ring 53 would serve the similar purpose ofreplacing or of supplementing the repulsive magnetic poles of magnets 56and 57 described below. Such thrust bearings may provide one or both ofradial and axial support for the rotor and serve to increase theresistance to shock loading thereby improving rotor stability.

Hydrodynamic thrust bearings on the outer periphery of the rotor providegood surface washing. Centrifugal forces created by thrust bearings tendto push fluid toward the periphery of the housing interior, providingincreased blood flow, which can improve the pump's resistance tothrombosis. In contrast, hydrodynamic bearings in the prior art whichare closer to the axis of rotation have reduced surface washing,resulting in a greater possibility of blood coagulation. Thus, since bythis invention, conditions are provided that reduce blood coagulation, alower amount of anticoagulant may be used with the blood pump andpatient, which may result in fewer patient adverse side effects. Ifdesired, hydrodynamic thrust bearing surfaces may be aligned in ahelical fashion on IS the surfaces of the rotor to improve surfacewashing by the moving blood as the rotor spins.

As an alternative to hydrodynamic thrust bearings acting axially on therotor, permanent rotor retaining magnets maybe placed in each land area35 within the lead, trailing or both ends of the rotor. One or morecorresponding permanent magnets may be placed within or on the tubularpump housing adjacent each rotor retaining magnet to effect repulsivemagnetic forces acting to retain the axial alignment of the rotor withinthe housing. By way of example only, a permanent magnet 56 is shown inFIGS. 1 and 2 in dotted lines on a land surface area at the trailing endof the rotor 14. A corresponding permanent stator magnet 57 is emplacedwithin the enclosure 40 surrounding the tubular housing 12. The rotormagnet 56 may be formed by magnetizing suitable rotor material. If thenorth poles of the rotor magnet 56 and the stator magnet 57 are adjacentor face each other, as shown in FIG. 1, the repelling magnetic forceswill assist in retaining the rotor in the proper axial position.Longitudinal or axial movement of the rotor to the right is therebyrestricted by the repulsive action of magnets 56 and 57. Of course,magnetic south poles could be directed to face each other in similarmanner, to achieve a generally similar effect. It will be understoodthat the magnet 57 may comprise a ring magnet or an electromagneticcoil.

With reference to FIG. 8A, in one embodiment, each of the thrust bearingsurfaces is provided with shrouds 49 provided along each lateral side ofa thrust bearing surface. These shrouds, defined by sidewalls ofdecreasing height created by the recessed portion of each bearingsurface, reduce the amount of fluid leakage from the bearing surface,and allow the development of higher radial pressure levels. Thereduction of such leakage to acceptable levels by means of such shroudscan almost double the load carrying capacity for the bearings.

An optional pressure relief surface downstream of each rotor thrustbearing surface may be provided to reduce hemolysis. This pressurerelief surface consists of a portion of the peripheral land area that iscontiguous with the rear end 48 of a thrust bearing surface and slightlydiverges away from the housing wall. Blood passing over the thrustbearing surface is thereby directed across the pressure relief surfaceinto an adjacent one of the grooves 22 formed in the rotor. Roundedsurfaces 54 at the leading end of the rotor, seen in FIGS. 7 and 8,facilitate entry of blood into the flow channels of the rotor. Thus, anaxial flow pump having wide peripheral land areas and utilizing shroudedhydrodynamic thrust bearings for radial or axial support is provided,having significant advantages over the known types of axial flow bloodpumps.

In some embodiments, the rotor 14 may be produced by either machining,molding, or casting a single piece of ferromagnetic material, such ascompression bonded neodymium or Alnico (aluminum-nickel alloy), or analloy of about 70-80 percent by weight of platinum and about 20-30percent by weight of cobalt. In some embodiments, from essentially 76-79percent by weight of platinum is present in the alloy. In someembodiments, the alloy may contain essentially from 21-24 percent byweight of cobalt. In one embodiment, an integral, one-piece rotorconsists of essentially 77.6 percent by weight of platinum and 22.4percent by weight of cobalt. Such a rotor is conventionally heat treatedto achieve good magnetic properties, and may be magnetized, with Northand South magnetic poles, as desired.

An advantage of such a rotor is that a single, integral piece made fromthe platinum and cobalt alloy can be easily fabricated into complexshapes, using conventional metal working and casting methods. Also, suchan alloy is magnetically isotropic, so that parts can be easilymagnetized with a plurality of magnetic poles in any geometricorientation. These characteristics allow the rotor to be fabricated froma solid piece of the alloy, thus eliminating the need to buildassemblies of magnets and support structures, as in the case of priorart ventricular assistance devices, with a resulting reduction ofmanufacturing costs. Additionally, the alloy used in this invention isbiocompatible, and has high resistance to corrosion, also having aRockwell hardness on the order of 31 Rc, which eliminates the need for ahard, outer coating. It will be understood that the rotor material maybe isotropic or anisotropic, as desired.

After fabrication, the rotor may be treated with a conformal, protectivepolymer coating of an organic polymer such as Parylene, or silicone, toprevent against oxidation by forming a hermetic seal around the rotor.On top of this, a hard, lubricious protective coating may be appliedover the conformal polymer coating, to protect against wear andabrasion. Such coatings may include chromium nitride, titanium-nitride,or other commercially available coatings such as ME92, Med Co 2000, orDLC. Alternatively, as stated above, the use of a biocompatiblemagnetically isotropic alloy such as a platinum-cobalt alloy obviatesthe use of the protective coating. Designed for a permanent heartventricular assist device, such a rotor could be a cylindrical devicehaving a 10 millimeters outer diameter and 20 millimeters length,providing flow rates of 2-10 liters per minute against physiologic,differential blood pressures. Magnetization of the rotor land sectionsmay occur before or after a coating application.

With reference to FIG. 8B, an embodiment of the rotor 14 includesrecesses 35A formed in each of the land areas 35, each of which recessescontains a cavity 55. Each cavity 55 is adapted to receive a discretepermanent drive magnet 73. The permanent drive magnets 73 serve the samepurpose as the magnetized areas 34 described above in connection withFIG. 2. In this embodiment, the land area recesses 35A include cavities74 adjacent each of the cavities 55. The cavities 74 are adapted toreceive discrete permanent retaining magnets 75 which serve the functionof the rotor retaining magnets 56 described above in connection withFIGS. 1 and 2. The land area recesses 35A also include bores 76 formedfor the purpose of weight reduction and to achieve dynamic rotationalbalance in the rotor when desired. A contoured cover 77 is adapted to beinserted into each of the land area recesses 35A to retain the discretedrive magnets 73 and retaining magnets 75 in position on the rotor. Inthis embodiment the covers 77 contain the hydrodynamic thrust bearingsurfaces 44 and 46 for the rotor described above in connection withFIGS. 7, 8 and 8A.

Referring to FIG. 9, there is disclosed an embodiment of the pump ofFIG. 1 having a sleeve 70 inserted within the outlet of the housing 12and having a reduced internal diameter area 71. The reduced internaldiameter area 71 serves as a stop to mechanically retain the rotor 14against ovement in one axial direction, to the right in FIG. 9, so thatmagnets 56 and 57 may be unnecessary. In addition, the reduced internaldiameter configuration of the sleeve 70 renders this arrangementsuitable as a pediatric version of the axial flow pump of this inventionas it will result in a reduced flow rate compared to an unsleavedconfiguration.

Referring to FIG. 10, a ganged series of axial flow blood pumps 60 has acommon, cylindrical housing 62 in which a plurality of rotors 14 c aremounted on a common shaft 64 in spaced-apart axial relationship. In onesuch embodiment, the rotors are commonly driven by the shaft 64 torotate as one. Such a device is described in co-pending application Ser.No. 11/118,551, the content of which is incorporated herein byreference. Each of the rotors 14 c has peripheral land areas 35 c,similar to the land areas 35 of the previous embodiments. By this means,added pumping power can be provided in the form of a multiple stagepump, with the rotors in series connection. Accordingly, a high capacitypump of smaller diameter can be provided.

Motor stators 36 c, comprising electrically conductive coils areprovided, one for each rotor, so that each of the respective rotorsperforms in a manner similar to that of the rotors described forprevious embodiments, but for their connection with the common shaft.The rotors 14 c and stators 36 c may be of the same design as any of theprevious embodiments, however, each rotor need not have the same numberof grooves or land sections between the grooves.

Stator blades 66 of traditional thin blade design may be mounted toextend radially inwardly from the inner wall of pump housing 62downstream of at least two of the three ganged rotors, although suchblades are not normally required in the axial flow pumps of the presentinvention. The stator blades 66 serve to diminish the rotationalmomentum of the axial flow output from the rotors before the flowencounters the next rotor. This arrangement permits more hydraulic workto be added to the blood or other fluid. Any desired number of thesegenerally radially extending blades 66 may be provided, if desired.Moreover, if desired, the leading or trailing end of each of the statorblades 66 may be provided with suitable hydrodynamic thrust bearingsurfaces to provide additional axial support to the rotor. The statorblades 66 may also include integral permanent magnets to define magneticbearings to support the rotor. Permanent magnets mounted in or on theappropriate leading or trailing ends of each rotor can provide repulsivemagnet poles to assist in the axial stability of the rotors.

In the embodiment shown in FIG. 10, each of the motor stators 36 c isaxially aligned with its corresponding rotor. Such alignment may bealtered to accommodate magnetic coupling or magnetic repulsion toprovide extra axial magnetic support.

Referring to FIG. 10A an alternative multi-rotor axial pump consists ofa plurality of blood pumps 60 each of which has one of the pump rotors14 c having the characteristics of the rotors 14 described above. Therotors 14 c are axially aligned in spaced-apart relationship and adaptedto pump blood or other fluid consecutively through the commoncylindrical housing 62 made of biocompatible material that exhibitsminimum eddy current losses, as described above in connection withsingle rotor pumps. In this embodiment, the individual rotors 14 cfunction independently without a connecting shaft. Motor stators 36 ceach comprise an electrically conductive coil as in the previousembodiments, one for each rotor, so that the respective rotors performin a manner similar to that of the previous embodiments. The stators 36c also may be of a design as previously described. The multiple rotors14 c acting in concert provide added pumping power and therefore enablesa high capacity pump of smaller diameter than a single stage pump, andmay be adapted for implant directly into the vascular system of apatient and otherwise reduce patent trauma.

In one embodiment, the independently rotatable rotors 14 c rotate at thesame rate. It will be understood that the rates of rotation of themultiple rotors may vary, one from the other, as desired. In someembodiments, one rotor may rotate clockwise, and be oriented such thatits grooves tend to drive blood or other fluid through tubular housing62 in the direction of arrow 63. An adjacent rotor may be oriented suchthat its grooves tend to drive blood in the same direction 63 uponcounterclockwise rotation. Thus, the multiple rotors work together todrive fluid in direction 63, even while they rotate in oppositedirections. An advantage of this arrangement is that a rotor rotatingcounterclockwise downstream from a clockwise rotating rotor tends tocounteract the rotational momentum imparted to the pumped fluid by theupstream rotor. This permits more hydraulic work to be added to thefluid. Depending upon the power applied to the individual stators 36 c,the respective rotors maybe driven at rotation rates which are similar,or different from each other, as may be desired. Adverse affects frommisaligned motor drive waveforms are thereby reduced.

In some embodiments, the multi-rotor pump is free of stationary, swirlsuppressing blades positioned within the housing and between the rotors.A need for such blades is diminished by counterrotating characteristicsof the respective rotors.

In some embodiments, more than two rotors are present. Adjacent rotorswill rotate in opposite directions from each other, so that clockwiserotating rotors are interspersed with counterclockwise rotating rotorsin axially alignment within the pump housing.

A permanent ventricular assist device of multistage configuration asdescribed above could have an outer diameter of six millimeters and alength of 15 millimeters, to provide flow rates of 2-8 liters per minuteagainst physiological differential pressures, as previously described.Such a multi-stage pump could be used as a peripheral vessel bloodinsertion pump, operating outside of the body, or provide bi-ventricularsupport and even total artificial heart action. It will be understood,that the multiple rotors need not be ganged on a common shaft and thatthe motor stator for each rotor could be energized to effect clockwiseor counterclockwise rotation of each rotor independently of therotational spin of other adjacent rotors.

FIG. 11 is an exploded view of an alternative blood pump configurationaccording to an embodiment of the present invention. The pump maycomprise a primary outer cannula-like enclosure 102 a and a secondary ordischarge section 102 b that fit together to seal a tubular housing 104and a surrounding motor stator 110 in place within the assembledenclosure. An O-ring 124A may be used to prevent blood from leakingbetween the inner tubular housing 104 and the enclosure 102 a. In thisembodiment, the entire tubular housing and surrounding motor stator areenclosed with the cannula-like structure have an inlet opening 105 ofreduced diameter, which provides a bullet-like configuration.

The motor stator 110 has three electrical cables 103 (seen best in theenlarged view of the motor stator in FIG. 11A) for three phase operationof the motor coils. The electrical cables may be contained within asuitable cable conduit comprising the three sections 120 k 120 a and 120b. It will be understood that other motor designs may be selected forapplications requiring high speed communication or increased efficiency,without departing from the scope of the invention.

FIGS. 12-16 depict an embodiment of a blood pump in which the rotationalkinetic energy of the axial flow of blood discharged by an axial flowpump is converted into a pressure flow at the outlet of the pump by avolute, indicated by reference numeral 106. While the incorporation of avolute is not necessary with the axial flow pump of the presentinvention, it is an optional embodiment for improving blood flowcharacteristics to further minimize thrombus formation and increasepressure of the pumped blood as it enters the vascular system.

Referring to FIGS. 12 and 13, a blood pump 100 comprises a substantiallycylindrical outer enclosure or cannula 102 a. The cannula 102 a may havethe slightly rounded or bullet shaped front or inlet end 105 of reduceddiameter having inlet 116 through which blood enters the pumpingchamber. The pumping chamber is defined by the substantially tubularinterior housing 104 having an external diameter smaller than theinternal diameter of the cannula. The cannula 102 a and tubular housing104, as described above, may be made of a biocompatible non-magneticmaterial such as titanium or ceramic.

The motor stator ring 110 may be located on the outside the housing 104and within the cannula 102 a in the annular space formed between thehousing 104 and the cannula 102 a. The three phase control wires for thecoils of the stator ring 110, described in detail above, are connectedthrough the power and control cable conduit 120 k that exits the pumpthrough a port 118 which may be defined as part of the volute 106. Arotor 108, of the type described in detail above, may be magnetically orhydrodynamically suspended in operation within the housing 104 andcentered within the stator ring 110 to provide an axial flow of theblood or fluid entering the inlet 116.

The volute 106 is sealed to the cannula 102 a and the tubular housing104 in a fluid-tight connection such that blood pumped by the rotor 108is moved into a central chamber 114 (FIG. 12) of the volute 106. Withreference to FIGS. 12 and 14, an O-ring 124B may be used to ensure afluid-tight connection of the volute to the inner tubular housing 104.One or more screws 126 may be used to secure a hermatic connection.

As depicted in FIGS. 15 and 16, the volute chamber 114 may be annular incross section as defined by a downstream center post 112 projectinginwardly along the pump axis from the base of the volute along therotational axis of the pump rotor 108. The center post 112 extendstoward but does not contact the downstream end of the rotor 108, and maybe a dome-topped cylinder (as shown in FIGS. 12, 14 and 15) or may beanother shape that serves to affect the flow of blood discharged fromthe pump rotor, as described in detail below.

Blood driven by the rotor 108 and entering the volute chamber from thepump chamber of the axial flow pump has a rotational or spiralingmomentum around the rotational axis of the rotor. The rotationalmomentum of the flow creates lower pressure areas in a central portionof the blood flow just downstream of the rotor. To some extent the lowerpressure area is alleviated by a tapered axial extension 24 (FIG. 1) atthe trailing edge 14B of the rotor. The center post 112 also tends tofill this lower pressure area in the downstream rotational blood flowcharacteristics as the blood enters the chamber 114 of the volute. Bloodthereafter fills the annular chamber 114 of the volute and the fluidpressure of the system causes the blood stream to flow in asubstantially centrifugal direction through the chamber 114 to thevolute discharge or outlet 122, depicted in FIGS. 13-16, therebyestablishing the output pressure. In this embodiment, the volute isbladeless and the discharge blood flow is in accord with thelongitudinal nature of the blood flow within the vascular system.Typically, a blood pump of this embodiment will be implanted such thatthe cannula portion traverses the apex of a heart ventricle, while thevolute portion remains outside of the heart. A graft (not shown) is usedto connect the discharge or outlet of the volute to an artery of thevascular system of the patient.

Referring now to FIG. 17, there is depicted an embodiment of acentrifugal volute 123 with an alternate configuration for a flowstraightner adapted to extend generally axially into the pump chamber ofan associated axial flow pump. In this embodiment, the volute 123 has aflow chamber 133 of generally circular cross section from which extendsa dual legged stator element 125 projecting out of the volute chamberand inwardly with respect to and along the axis of an axial pumpingchamber as described above (not shown). The stator element has a pair ofparallel legs 126 and 128 extending substantially co-axially with therotational axis of the pump. The inner end portions of each of thesupporting legs 126 and 128 are bent or curved such that the end portion130 of the leg 128 is curved to project at an angle of about 45° to thelongitudinal axis of the stator element 125 and the axis of anassociated pumping chamber. The inner end portion 132 of the support leg126 is also curved to project at angle of 45° to the pump axis. The axisof curvature of the end portion 130 is perpendicular to the axis ofcurvature of the end portion 132. The dual legged stator 125 acts tochange the kinetic rotational momentum of the blood flow output from theaxial pump to a pressure flow as the blood enters the centrifugalchamber 133 of the volute 123 before discharge through radial outlet134.

Referring to FIG. 18, there is shown still another embodiment of avolute 136 having a centrifugal flow chamber 137 of substantiallycircular cross section with a central axial flow straightener or statorelement 135 adapted to extend generally axially into the pump chamber ofan associated axial flow pump of the type described herein. The statorelement 135 consists of a center post portion 138 aligned with the axisof the axial flow pump (not shown) having a tip or end portion 139 ofgenerally rectangular shape. The short axis of the rectangular shapedstator tip is aligned and parallel with the axis of the center postportion 138 and the axis of the axial flow pump. The function of thestator element is, as described above in connection with the othervolute embodiments, to alter the kinetic rotational momentum of theoutflow from the pump to a pressure flow as the fluid fills the volutechamber and is pressured to discharge at the radial outlet 141.

Referring to FIG. 19, there is depicted yet another embodiment of acentrifugal volute 142 having a centrifugal flow chamber 143 of circularcross section. A flow straightener or stator element 144 extends fromthe base of the volute chamber axially inwardly along and substantiallyaligned with the axis of an associated axial flow pump (not shown). Thestator element 144 consists of a central post section 146 with a widedouble-tined end portion 147. Each of the tines extends generallyparallel to the axis of the center post 146, one on each side thereof.Blood exiting the axial flow pump with kinetic rotational momentum isconverted to a pressure flow by the stator element 144 before enteringthe volute chamber and being forced centrifugally to discharge from anoutlet 147.

In accordance with the present invention, blood outflow characteristicsmay be altered without the need for projecting blades or postsdownstream of the axial flow pump. Shaped passageways designed toimprove flow characteristics may be employed instead. With reference toFIGS. 20 and 20A, there is depicted a straight through flow straighteneraccording to one embodiment of the present invention. The flowstraightener has a base section 148 for securely connecting to the bloodpump. A straight cylindrical tube 149 may extend from the base section148. A passageway having a circular opening 151 may be shaped into anoval cross section with an oval outlet 152 formed within the tube 149 asshown in FIG. 20A. The opening of the shaped passageway 151 may be ofany shape helping to enhance flow characteristics. The shaped passageway161 defining the oval outlet 152 gradually ushers blood havingrotational momentum through the oval-shaped constraint to convert theflow to substantially axial flow. Alternately, the shaped passageway 151may be partially conical, having a circular, oval or other shaped outletsomewhat smaller in diameter than that of the inlet opening toaccomplish the same purpose. In this embodiment, the passageway is 151is straight and coaxial with the axis of the axial flow pump.

With reference to FIG. 21, there is depicted a flow straightenerembodiment according to a yet further embodiment of the presentinvention. The flow straightener of this embodiment has a base sectionfor securely connecting to the axial flow blood pump. A bent tube 153contains a constricted portion 156 which acts to diminish the rotationalmomentum of the axial blood flow output from the pump. The axial bloodflow from the tube 153 is discharged through an outlet 157 from which asuitable graft will connect the blood flow to the vascular system.

Referring to FIGS. 22, 22A and 22B, there is depicted yet anotherembodiment of a downstream flow straightener according to the presentinvention. The flow straightener has a straight cylinder tube 158 havinga flow chamber 158A and a base 159. A blade carrying center post 161extends axially through at least a portion of the flow chamber 158A andextends axially into the pump chamber of an associated axial flow pump.In one embodiment, the center post 161 is affixed to the inner sidewallof the flow chamber 158A at a point of connection 162. (FIG. 22A). Thesupport for the centerpost 162 may be a radially extending connectingarm 161 A that need not traverse the entire diameter of the flowchamber. The post 161 may be of any shape, but is here depicted as adome-topped cylinder having a pair of symmetrical diametrically opposed,contoured and pointed blade sections 163 extending longitudinally alongat least part of its length and beyond by a predetermined amount. Theblade sections 163 may protrude like rabbit ears beyond the top of thecenter post and may curve in opposite directions away from the axis ofthe center post 161 as depicted in FIG. 22B. The purpose of thisconfiguration is also to diminish the rotational momentum of the axialflow output from the pump.

Referring to FIGS. 23 and 23A, there is depicted a downstream flowstraightener with a simplified flow-straightening blade element 164according to another embodiment of the present invention. In thisembodiment, a straight cylindrical tube section 166 is connected to abase 167. The tube 166 is affixed at the output from an axial flow pumpand defines an internal flow chamber 168. The flow-straightening bladeelement 164 projects radially inwardly from an inner sidewall of theflow chamber 168. The blade element 164 may be suitably welded to thesidewall of the flow chamber or be formed together with and as part ofthe tube section 166. The blade element 164 is configured with atransverse axis aligned parallel to or co-axial with the axis of theflow chamber 168. In one embodiment the blade element 164 terminates atabout the longitudinal centerline of the flow chamber 168 (FIG. 23A). Itmay, however, traverse completely across the flow chamber along adiameter (not shown) without departing from the scope of the presentinvention. The axis of the longitudinal tube section 166 is co-axialwith the axis of the axial flow pump. The blade 164 may be substantiallywedge-shaped and may be short (as shown) or longer. For example, theblade 164 may extend axially through the entire length of the tube 166and may even extend beyond the length of the tube 166, as desired.According to an embodiment of the present invention, two rotary pumps asdescribed herein may be combined to form an artificial heart that may beused to completely replace the natural heart in a patient suffering fromheart failure.

Referring to FIG. 24, an artificial heart is shown using rotary axialflow blood pumps of the type described herein. In one embodiment, theartificial heart may comprise a first section 181 for pumping blood tothe patient's aorta and a second section 182 for pumping blood to thepatient's pulmonary artery. Each section 181 and 182 may contain a pump10 as described in detail above. The first section 181 may include afirst inflow 183 and a first outflow 185. The second section 182 mayinclude a second inflow 184 and a second outflow 186.

The inflows 183 and 184 may be made of a penetrable material such as asoft Dacron texture material so that it may be easily sutured to thepatient's circulatory system. The inflows 183 and 184 may have a shapethat is wider at the end that is connected to the patient's circulatorysystem than at the end that is connected to the pump 10. The inflows 183and 184 may be elbowed so that the inflows 183 and 184 may be proximalto the outflows 185 and 186.

The first pump section 181 and the second pump section 182 may beattached together by a connecting member 180 such as a bracket or thelike.

In this embodiment, the artificial heart does not require artificialvales thereby improving device reliability.

A balance member or atrial shunt or shunt may optionally be connectedbetween the first and second inflows 183 and 184 to substantiallyequalize or balance the flow of blood through the first and secondinflows 183 and 184. Thus, when the pressure in the first and secondinflow members is unbalanced, blood may be shunted between the inflowmembers. The shunt may include two ends where one of the ends isconnected to the first inflow 183 and the opposing end of the shunt isconnected to the second inflow 184. The shunt 124 may be integrallyformed with each of the inflows 183 and 184. The shunt may automaticallyequalize or balance the hydraulic blood flow through each of the firstand second sections 181 and 182. The shunt may therefore prevent oneside of the artificial heart from over pumping the other side of theheart

The first section 181 may be designed to pump more blood than thesection 184. According to one embodiment, the first section 183 isdesigned to pump 15% more blood than the second section 182.

Power and control cables 120K may be used to power and control each pump10.

The above specific embodiments are illustrative, and many variations canbe introduced on these embodiments without departing from the spirit ofthe disclosure or from the scope of the appended claims. For example,elements and/or features of different illustrative embodiments may becombined with each other and/or substituted for each other within thescope of this disclosure and appended claims.

1. A blood pump, comprising: a pump housing; a rotor for pumping bloodpositioned in said housing, said rotor having an axis of rotation and aleading edge and a trailing edge and comprising peripheral land surfacesdefined by one or more flow channels extending from said leading edge tosaid trailing edge, said channels being curved to drive blood in anaxial direction as the rotor is rotated, the collective width of saidchannels at some axial positions on the radial periphery of the rotorbeing substantially equal to or less than the collective total width ofsaid peripheral land surfaces; and a motor including a plurality ofmagnetic poles carried by the rotor, and a stator including anelectrically activated coil to magnetically interact with said magneticpoles to cause said rotor to rotate.
 2. The blood pump of claim I inwhich peripheral land surfaces comprise hydrodynamic thrust bearingsurfaces.
 3. The blood pump of claim 2 in which said bearing surfacescomprise shroud sidewalls extending substantially transverse to therotation axis of the rotor.
 4. The blood pump of claim 2 comprising atleast one magnetic bearing formed between said rotor and said pumphousing to position said rotor.
 5. The blood pump of claim 1 in whichsaid rotor comprises one or more permanent magnetic poles in said landsurfaces, the motor being of the radial flux gap design, whereby axial,magnetic forces hold the rotor in position.
 6. The blood pump of claim 1in which the motor comprises a hermetically sealed tubular stator thatslides over said pump housing and is secured thereto.
 7. The blood pumpof claim 1 in which said pump housing is cylindrical.
 8. The blood pumpof claim 1 in which said rotor comprises at least one permanent magnetmounted therein.
 9. The blood pump of claim in which said pump housingis made from biocompatible titanium or ceramic.
 10. The blood pump ofclaim l which comprises a plurality of said rotors axially spaced apartwithin said pump housing, each of said rotors having one of said motorsto cause said rotors to rotate.
 11. The blood pump of claim 9 in whichsaid housing is adapted to exhibit minimum eddy current losses.
 12. Theblood pump of claim 10 in which radially extending stator plates areprovided between said rotors.
 13. The blood pump of claim 1 in whichsaid rotor has a conformal polymer coating defining a hermetic seal toprevent oxidation.
 14. The blood pump of claim 13 comprising a hard,lubricious protective coating over said conformal polymer coating toprotect from wear and abrasion.
 15. An axial-flow blood pump for pumpingblood, comprising: a substantially cylindrical outer enclosure; atubular housing concentric with and located within said outer enclosurehaving at one end an inlet and at an opposite end an outlet; a motorstator concentric with and located between said outer enclosure and saidtubular housing; an impeller concentric with and located within saidtubular housing, suspended in operation by a combination of passivemagnetic forces between magnets within said impeller or magnetizedregions of said impeller and said motor stator and hydrodynamic thrustforces generated as blood flows between said tubular housing and aplurality of hydrodynamic thrust bearing surfaces located on saidimpeller; and a volute in fluid-tight connection with said outlet ofsaid tubular housing for receiving blood in the axial direction anddirecting blood in a direction normal to the axial direction, whereinsaid volute has a flow-improving member extending axially from thevolute and into and coaxially with said tubular housing.
 16. Anaxial-flow blood pump for pumping blood, comprising: a substantiallycylindrical outer enclosure; a tubular housing concentric with andlocated within said outer enclosure having at one end an inlet and at anopposite end an outlet; a motor stator concentric with and locatedbetween said outer enclosure and said tubular housing; an impellerconcentric with and located within said tubular housing, suspended inoperation by a combination of passive magnetic forces between magnetswithin said impeller or magnetized regions of said impeller and saidmotor stator and hydrodynamic thrust forces generated as blood flowsbetween said tubular housing and a plurality of hydrodynamic thrustbearing surfaces located on said impeller, and a flow straightener ordiffuser in fluid-tight connection with said outlet of said tubularhousing for receiving blood in the axial direction and directing bloodin said axial direction or in a direction normal to the axial direction,wherein said flow straightener has one or more stator blades therein.17. A rotor for an axial flow pump, the rotor comprising: a cylindricalbody for moving fluid in the direction of an axis of rotation thereof,said cylindrical body having a leading edge portion for engaging fluidand a trailing edge portion for discharging fluid, and having one ormore flow channels formed in the periphery thereof to conduct fluid fromsaid leading edge portion to said trailing edge portion, said one ormore flow channels being curved around the axis of rotation of thecylindrical body to impart rotational momentum to fluid being movedaxially therethrough and discharged therefrom during rotation of therotor; and arcuate land area surfaces on the periphery of saidcylindrical body having edges defining said one or more of said flowchannels, said land area surfaces having predetermined magnetic polesfor interaction with magnetic flux external to the rotor wherebyrotational movement ay be imparted to the rotor.
 18. The rotor of claim17 comprising a plurality of said flow channels, each of which defines afluid entry section at said leading edge portion of the rotor and afluid exit section at said trailing edge portion of the rotor.
 19. Therotor of claim 18 in which each of said flow channels has a centralsection substantially narrower than the other sections thereof.
 20. Therotor of claim 18 in which said fluid exit section extends substantiallyaxially with respect to the axis of rotation of the rotor.
 21. The rotorof claim 18 in which said fluid exit section of each of said flowchannels is wider than said fluid entry section.
 22. The rotor of claim17 in which each of said land area surfaces comprises a substantiallyarcuate thrust bearing surface having a tapered portion extending from alow point at one of said land area surface edges to a high point on theperiphery of said cylindrical body.
 23. The rotor of claim 22 in whichthe axis of curvature of said tapered thrust bearing surface is notcoaxial with the axis of rotation of said cylindrical body.
 24. Therotor of claim 23 in which each of said land area surfaces comprises twoor more of said arcuate thrust bearing surfaces, the axes of curvatureof said thrust bearing surfaces being substantially parallel.
 25. Therotor of claim 22 in which said thrust bearing surfaces are defined oneach side by a sidewall shroud extending from a high point at one ofsaid land area surface edges to merge into the periphery of saidcylindrical body.
 26. The rotor of claim 25 in which the periphery ofsaid cylindrical body downstream of each of said thrust bearing surfacesis curved away from said thrust bearing surface to define a pressurerelief surface for fluid flowing from said thrust hearing surface. 27.The rotor of claim 17 in which the rotor is provided with a plurality ofbores therein to provide dynamic balance during rotation thereof. 28.The rotor of claim 17 in which each of said flow channels is ofnon-uniform depth along its length from said leading edge portion tosaid trailing edge portion.
 29. The rotor of claim 1 in which said pumphousing comprises a material adapted to minimize eddy current losseswhen said rotor is rotated by said motor.
 30. The rotor of claim 1comprising a heat treated biomedical alloy.
 31. The rotor of claim 30 inwhich said alloy consists of platinum and cobalt.
 32. The rotor of claim31 comprising in the range of from 70 to 80% platinum by weight.
 33. Therotor of claim 30 comprising in the range of from 20 to 30% cobalt byweight.
 34. The rotor of claim 32 comprising in the range of from 76 to79% platinum by weight.
 35. The blood pump of claim 1 comprising therotor of claim
 17. 36. The blood pump of claim 35 in which one of saidleading and trailing edge portions of said rotor is provided withaxially retaining magnetic poles of one polarity.
 37. The blood pump ofclaim 36 in which said pump housing is provided with fixed magneticpoles of said one polarity positioned adjacent said axially retainingmagnetic poles of said rotor.
 38. The blood pump of claim 37 which isadapted to be implanted in the vascular system of a patient.
 39. Theblood pump of claim I in which said pump housing is tubular and theblood pump comprises a plurality of said rotors positioned in axiallyspaced-apart alignment within said pump housing.
 40. The blood pump ofclaim 39 in which said rotors are interconnected within said housing torotate together in the same direction on a common shaft.
 41. The bloodpump of claim 39 in which each rotor is suspended to rotateindependently within said housing without a common shaft.
 42. The bloodpump of claim 41 in which each rotor rotates in a different rotationaldirection from the immediate upstream and downstream adjacent rotors.43. The blood pump of claim 41 in which each rotor rotates at adifferent rotational speed from the immediate upstream and downstreamadjacent rotors.
 44. The blood pump of claim 39 in which each of saidrotors comprises a plurality of drive magnets and said motor comprises aradial flux gap design whereby magnetic forces suspend each rotor inaxial position within said housing.
 45. The rotor of claim 17 comprisingisotropic material.
 46. The rotor of claim 17 comprising anisotropicmaterial.